Modulator



Patented Nov. 15, 1938 MonULATon Hermann Bendel, Berlin, Germany, assigner to Siemens & Halske, Aktiengesellschaft, Berlin- Siemensstadt, Germany, a corporation of Germany Application. November 19, 1936, Serial No. 111,579 In Germany December 23, 1935 7 claims. (ci. 17e- 171) This invention concerns a new method of and means for suppressing undesirable frequencies 5 tiers having necessarily to possess perfectly equal characteristics. The method according to this invention consists in adding an unmodulated carrier current in the output circuit of the modulator which carrier is of the same frequency as the l carrier current to be modulated. The said additional carrier current causes a shift of the Working points of the rectiers. Inasmuch asV this shift in the several rectiers will not act in the same sense in each case, indeed, since in some rectiers it will add to the load, while in others it will subtract therefrom. the working point of the rectiers in reference (with respect) to the carrier current to be modulated may be varied inside certain limits.

If the amplitude and the phase of the carrier current to be added have been properly chosen,

proachedr by a use of the method here disclosed. that is to say, a state in which all of the rectiers will have practically the same working point and the same characteristic. Once this condition has been satisfied. not only the carrier current, but also the audio frequency current with which the rier` stated, it also so influences the working point of cal viewpoint, are obtained. 5

The invention shall be explained in more detail by reference to exemplied embodiments i1- lustrated in the drawing:

Figure i shows a balanced modulator with means for impressing carrier energy on the modul0 lator output to improve the operation,

Figures 2 and 3 are graphs illustrating how the improved operation is obtained; while Figures 4 and 5 are modulators of the type shown in Figure 1 with circuits for impressing l5 carrier energy on the modulated output.

Figure 1 shows a double push-pull modulator or a so-called ring modulator. U1 is the input transformer through which the audio frequency energy n is fed in. ll: is the output transformer 20 hand, another carrier current' i is introduced, thereby in the modulator circuit. The secondary 25 winding of the input transformer and the primary winding of the output transformer have center taps, and it is at these points that the carrier current to be modulated is introduced. The oxide-type rectiiiers i, 2, 3, Il. connected ring- 30 fashion carry the partial carrier currents iizaii. The amount of the carrier current for one alternation is ii-l-iz. and for the second alternation is-i-ii. Presupposng that the two rectiers I and 2 have like characteristics, thev current i1 and i2 a5 are equal. Il this assumption is .not fulfilled, then, for one alternation, a carrier current 2'1-1'2 will arise in the output circuit. The same thing holds good for the case where the characteristics of the rectiers 3 and l are not perfectly alike, 40

f for then for the second alternation or half-cycle there arises in the output circuit an equalizing current ia-.

In Figure 2 the characteristic of the rectifier l shall be indicated hy K1 and the characteristic 45 of the rectier 2 by K2. K1.: shall be assumed to be the shape of a characteristic situated between the two rectiers. If, then, according to Figure 1,

another carrier current z is fed to the transformer current by an amount i, while in the case of reati-- ner 2 it will occasion a growth of the carrier current by a like amount i. For the carrier current to be modulated, i1 and i2, the said superposition 1| whose action is a function of of i has the same effect as if both rectiilers had the same characteristic Km. The same situation holds good for the rectiflers l and I, although care must be taken so that for these rectiiiers. by the added current i, there will also be caused a new characteristic Ku located approximately midway between lthe two characteristics. Under certain circumstances, it may be necessary to the said end to interchange or transpose the rectifiers 3 and 4.

If the audio frequency current in the output circuit is to be suppressed completely, then the characteristics Ki.: and Ku will have to register or coincide. However, in the majority of instances. this will not be feasible. Thus, a balance or residue of audio frequency current will still be present in the output circuit of the modulator. and while this current has been essentially reduced, it is still discernible, even if the carrier current could be completely suppressed. By regulation of the size and phase of the added carrier current i it is readily possible to adjust to optimum or most favorable values according to whether it is felt to be more 'desirable or necessary to accomplish complete suppression of the carrier current or of the audio frequency current in the output circuit.

Now. the method hereinbefore described offers this further advantage that also the harmful effeet of harmonics frequently present in the carrier wave generator may be eliminated inside wide limits by the addition of the carrier current i as hereinbefore suggested. Figure 3 shows the shape of the carrier frequency w, of the harmonic 210 and the resultant potential w+2w. It can be readily seen from the figure that the maximum currents of w+2w may be very different for the two `alternations seeing that the absolute value of the harmonic becomes added to the fundamental wave during one alternation, while for the other alternation is subtracted. Also in this instance the method according to this invention can be used to provide a ready remedy inasmuch as the added carrier current i for corresponding rectifiers will become added in one of them and be subtracted for the other rectifier. If the signs are properly chosen, the influence of the harmonics by the added carrier current i can be equalised or at least be diminished.

Figure 4 shows a practical embodiment of the invention. 'Ihe radio frequency generator H by way of transformer Us feeds directly the ringtype modulator. Connected with the secondary winding of the said transformer Ua is a diilerential bridge comprising r1 and the further resistance n and resistance n inserted in the diagonal of the bridge arrangement. Connected in parallel to the resistance rz is moreover a variable condenser c which has the to regulate the phase of the current i. 'I'he amplitude may be regulated in fine steps by resistance n and coarsely -by the tap of n. n and n indicates the resistance of the input and the'load circuit.

Figure 5 shows another exemplified embodiment which differs from the one shown in Figure 4 essentially in that the diilerential bridge is not connected directly with the secondary circuit of the transformer Us, but rather in parallel relation to a resistance rs which is traversed by the carrier current to be modulated. If n -is linear in nature, then the added current i and the current to be modulated proportion. However, in some instances it is convenient to make the resistance of material temperature and to be modulated the regulable resistance y will vary in likey thus of current. The result is that the carrier current i is adapted to the temperature variations of the rectifier elements to a large degree.

In both exemplified embodiments the carrier current i to be added is derived from one and the same generator H as the carrier current to be modulated. This oiers tage that in the case of fluctuations of the generator voltage, these will similarly act upon the carrier current to be modulated as well as on the added or supplemental carrier current. The output transformer U2 is then used not only to deliver the modulated current to the load circuit, but also for the purpose of introducing the additional carrier current i into the modulator. It would also be feasible to provide besides transformer Uz anothertransformer which solely serves the purpose'to introduce the additional carrier i into the modulator. On the other hand, it would also be feasible to equip transformer U2 with a third Winding which would serve only for feeding in the carrier current i. The method hereinbefore described may be used in a similar way not only for a double push-pull modulator as here suggested, but also in simple or plain push-pull modulator circuit organizations.

I claim:

v l. In a modulation system, a pair of rectiiiers, an output circuit connected between corresponding electrodes of said rectiilers, means for impressing wave energy to be modulated in phase on like electrodes of said rectiers, means for impressing modulating energy in phase opposition on like electrodes of said rectiilers, and additional means for additionally impressing Wave energy in phase displad relation on like velectrodes of said rectiers to control the operating characteristics of said rectifiers in a sense such that their characteristics are made similar.

2. In a modulation system, a source of wave energy to be modulated, a source of modulating wave energy, a pair of rectiilers, a circuit coupling said source of wave energy to be modulated in phase to like electrodes of said rectiiiers, a circuit coupling said modulating wave energy in phase displaced relation to like electrodes of said rectiners, an output circuit connected between like electrodes of said rectiflers, and a circuit including amplitude regulating and phasev adjusting elements coupling said source of wave energy to said like'electrodes coupled with said output circuit to control the operating characteristics of said rectiflers in a sense such that their characteristics are similar.

l3. A modulation system as recited in claim 2 wherein one of said 'amplitude regulating elements is non-linear in character.

4. An arrangement as recited in claim 2 wherein an additional pair of rectifiers are crossconnected between the electrodes of said first named pair of rectiilers. y

5. In a balanced modulation system, a pair of rectifiers having input and output electrodes, two sources of wave energy to be superimposed, an output circuit'connected with corresponding electrodes of said rectifiers, means for impressing wave energy from one of said sources in phase on the special advanlike electrodes of said rectiers, means for impressing wave energy from the other of said sources in phase opposition on like electrodes of said rectifiers whereby wave energycharacteristic of both of said sources appears in said output circuit, and undesired wave energy related in fre- In a balanced modulation system, a pair of 6. rectiiiers having input and output electrodes,l two tion circuit, in which wave energy characteristic of the combined wave energy of said sources and 7. A system as recited in claim 6 non-linear resistance 1s connected in series with HERMANN BENDEL. 

